The disclosed invention relates generally to surgical implements and methods used in spinal surgery, and more particularly to an expandable implant for stabilization of vertebrae and a method for stabilizing vertebrae.
Chronic back pain is one of the most common and perplexing problems facing the field of orthopedic surgery. In addition to patient discomfort, chronic back pain has severe adverse societal impacts including lost income, decreased involvement in family and community life, as well as possible chronic dependence on drugs and/or alcohol. In many cases, back pain can be avoided by preventing relative motion between spinal vertebrae, a therapy commonly referred to as intervertebral stabilization.
Surgical techniques are known for use in intervetebral stabilization. These surgical techniques seek to rigidly join vertebrae separated by a degenerated disk. Ideally, the surgery effectively replaces the vertebra-disk-vertebra combination with a single rigid vertebra. Various surgical techniques have developed which attempt to approach or approximate this ideal.
One technique known in the art is to place either bone or nothing into the space left after removing a damaged disk. Placing nothing in the space allows the space to collapse which may result in damage to the nerves. With this technique, the space may also fill with scar tissue and eventually lead to a reherniation. The use of bone is less than optimal. If the bone is obtained from the patient, additional surgery is required and the bone is of limited availability in its most useful form. If the bone is obtained elsewhere, the bone may lack living bone cells, carry a significant risk of infection, and/or is also limited in supply since it is usually obtained from accident victims. Furthermore, the bone only provides marginal structural support and lacks a means to either stabilize itself against dislodgement, or to stabilize the adjacent vertebrae.
Another technique involves the use of an implant which, acting alone or in combination with bone fragments, replaces the use of bone grafts. The implants are sometimes expandable to contact adjacent vertebrae and achieve vertebral fusion after a sufficient amount of bone growth occurs. While conventional implants can be filled with bone fragments to expedite bone growth, it is believed that the mere presence of the bone fragments is not enough to achieve the rate of bone growth that would be provided if the bone fragments or any other osteogenic material were extruded from the implant during expansion of the implant.
Whether or not bone fragments or other osteogenic material are used, many implants are less than satisfactory for supporting healing vertebrae after implantation. When a circular bore is drilled into the intervertebral disk space and also into adjacent portions of the vertebrae above and below the intervertebral disk space, many prior art implants provide less than fully satisfactory support to the undrilled, rigid outer surface portions of the vertebrae. As a result of this less than fully satisfactory support, more spinal support structures may be needed, or each of the vertebrae may tilt from side to side, eventually causing spinal misalignment.
Those skilled in the art will appreciate that there is a need for an expandable intervertebral implant which is adapted to extrude osteogenic material during its expansion and to expedite the bone growth and fusion process than compared to the prior art. By expediting the bone growth and fasion process, it is possible to reduce the amount of time between surgery and the patient""s ability to return to work or perform physically demanding activities.
Those skilled in the art will also appreciate that there is a need for an expandable intervertebral implant which is adapted to expand against cancellous bone tissue surfaces of vertebrae while providing improved support to vertebrae during the bone growth and fusion process. By providing expansion and improved support, it is possible to reduce the risk of spinal misalignment and decrease the need for additional spinal support structures.
The disclosed invention is just such an implant and achieves the advantages and overcomes the disadvantages of the prior art through use of an expandable intervertebral implant. The expandable intervertebral implant of the present invention extrudes osteogenic material during expansion, and includes a curvalinear shoulder for improved support of vertebrae during the bony growth and fusion process.
It is an object of the invention to provide an expandable implant that will extrude osteogenic material during expansion thereof and which will provide improved support of healing vertebrae during the bony growth and fusion process.
It is another object of the invention to provide an expandable implant that will expand against cancellous bone tissue of a vertebrae while providing improved support of a periosteal membrane surface of the vertebrae during the bony growth and fusion process.
It is yet another object of the invention to provide a method of stabilizing first and second vertebrae with respect to one another that will expedite the bony growth and fusion process while reducing the risk of spinal misalignment.
An expandable intervertebral implant pursuant to the present invention is adapted to be inserted at least partially into vertebrae or in between two vertebrae, and is adapted to be secured thereto by expansion. The implant comprises a first shell, a second shell, and at least one extrusion opening. The first shell has a first end and a plurality of engaging members extensible from the implant for engagement with cancellous bone tissue of a vertebra. The engaging members axially extend from the first end. A cross section of the first shell includes at least one curvalinear shoulder for supporting a periosteal surface of a vertebra. The second shell is operatively connected to the first shell and has a second end with at least one bearing surface engageable with the engaging members. A cross section of the second shell including at least one curvalinear shoulder for supporting a periosteal surface of a vertebra. The first and second shells cooperate to form a cavity delimited by inner surfaces thereof. There is at least one extrusion opening in at least one of the first and second shells. Movement of the second shell with respect to the first shell causes expansion of the implant and at least partial extrusion of material contained in the cavity through the extrusion opening.
An expandable intervertebral implant pursuant to the present invention is adapted to be inserted at least partially into a bore drilled between two adjacent vertebrae to expose cancellous bone tissue within each of the two vertebrae, and is also adapted to be secured to the vertebrae by expansion. The implant comprises first and second shells and first, second and third axes. The first shell has a first end and a plurality of engaging members extensible from the implant for engagement with the cancellous bone tissue of a vertebra. The engaging members axially extend from the first end. A cross section of the first shell includes at least one curvalinear shoulder for supporting a periosteal surface of a vertebra. A second shell is operatively connected to the first shell and has a second end with at least one bearing surface engageable with the engaging members. A cross section of the second shell includes at least one curvalinear shoulder for supporting a periosteal surface of a vertebra. The first axis extends between the first and second ends, while the second axis extends perpendicular to the first axis. The third axis extends perpendicular to the first and second axes, wherein the second axis has a length greater than a diameter of the bore and the third axis has a length less than the diameter of the bore.
A method for stabilizing first and second vertebrae with respect to one another pursuant to the present invention comprises the following steps. A bore is formed between two vertebrae to expose cancellous bone tissue in at least one vertebra. At least one expandable intervertebral implant containing osteogenic material is provided. The implant has first, second and third axes and first and second opposed shells. A cross section of the implant has at least one curvalinear shoulder for supporting a periosteal membrane of one of the two adjacent vertebrae. The first axis extends between the ends. The second axis extends perpendicular to the first axis and has a length greater than a diameter of the bore. The third axis extends perpendicular to the first and second axes and has a length equal to or less than the diameter of the bore. At least one of the first and second shells has engaging members extensible from the implant for engagement with the cancellous bone tissue, wherein the engaging members extend axially from an end of the at least one shell. The implant is inserted in the bore so that the curvalinear shoulder bears against and supports the periosteal membrane. The implant is expanded. An osteogenic material is extruded from the implant during expansion thereof.
These and other objects of the present invention will become apparent from the following detailed description and independent claims.
The invention may be best understood with reference to the accompanying drawings wherein an illustrative embodiment is shown.